The invention relates to a method of stabilizing a Ziegler catalyst component to prevent separation of the catalyst from the dispersing solvent for times sufficient to allow utilization of the catalyst dispersion prior to said separation.
Shirai et al, U.S. Pat. No. 4,086,185, teaches to pre-activate a titanium trichloride catalyst component by polymerizing a small amount of propylene onto the catalyst. A stable dispersion of the pre-activated catalyst in an inert solvent is formed. The resulting dispersion is useful to prepare polypropylene having reduced amounts of atactic polypropylene.
Kikuta et al, U.S. Pat. No. 4,287,328, teaches to pre-activate a catalyst for the polymerization of a propylene by pre-polymerizing a small amount of alpha-monoolefin onto the catalyst in the presence of an organoaluminum compound. The pre-activated catalyst had greater stability as measured by catalyst activity, crystallinity of the polypropylene, and the resultant shape of the polypropylene particles formed.
In copending application Ser. No. 454,224, filed Dec. 29, 1982, we described a catalyst for the preparation of low density polyethylene. The catalyst could be pre-activated by polymerizing a small amount of alpha-monoolefin on the catalyst in the presence of a single alkyl aluminum compound.
All of the above references have the disadvantage that a dispersion of catalyst in inert solvent must be constantly agitated while being added to a polymerization reactor along with monomers and co-catalysts. Without the agitation, the dispersions tend to rapidly separate into catalyst and supernatant solvent. The separation causes variation in catalyst concentration and difficulty in feeding the dispersion to a reactor.